The Israeli journalist Amira Hass describes the moment her mother, Hannah, was marched from a cattle train to the concentration camp at Bergen-Belsen. "They were sick and some were dying," she said. "Then my mother saw these German women looking at the prisoners. This image became very formative in my upbringing, this despicable 'looking from the side'."

It is time we in Britain stopped looking from the side. We are being led towards perhaps the most serious crisis in modern history as the Bush/Cheney/Blair "long war" edges closer to Iran for no reason other than that nation's independence from rapacious America. The safe delivery of the 15 British sailors into the hands of Rupert Murdoch and his rivals (until their masters got the wind up) is both farce and distraction. The Bush administration, in secret connivance with Blair, has spent four years preparing for "Operation Iranian Freedom". Forty-five cruise missiles are primed to strike. According to General Leonid Ivashov, Russia's leading strategic thinker: "Nuclear facilities will be secondary targets, and there are 20 such facilities. Combat nuclear weapons may be used, and this will result in the radioactive contamination of all the Iranian territory, and beyond."

And yet there is a surreal silence in Britain, except for the noise of "news" in which powerful broadcasters gesture cryptically at the obvious, but dare not make sense of it lest the one-way moral screen erected between us and the consequences of an imperial foreign policy collapses, and the truth is revealed.

"The days of Britain having to apologise for the British empire are over," declared Gordon Brown to the Daily Mail. "We should celebrate!" In Late Victorian Holocausts, the historian Mike Davis documents that as many as 21 million Indians died unnecessarily in famines criminally imposed by British policies. And since the formal demise of that glorious imperium, declassified official files make clear that British governments have borne "significant responsibility" for the direct or indirect deaths of between 8.6 million and 13.5 million people throughout the world - from imperial military interventions and at the hands of regimes strongly supported by Britain. The historian Mark Curtis calls these victims "unpeople". "Rejoice!" said Thatcher. "Celebrate!" says the paymaster of Blair's bloodbath. Spot the difference.

We need to look behind the one-way moral screen, urgently. Last October, the Lancet published research led by Johns Hopkins University in the US that calculated the deaths of 655,000 Iraqis as a direct result of the Anglo-American invasion. Downing Street acolytes derided the study as "flawed". They were lying. They knew that the chief scientific adviser to the Ministry of Defence, Sir Roy Anderson, had backed the survey, describing its methods as "robust" and "close to best practice", and that other government officials had secretly approved the "tried and tested way of measuring mortality in conflict zones". The figure of Iraqi deaths is now estimated at close to a million.

"This Labour government, which includes Gordon Brown as much as it does Tony Blair," wrote Richard Horton, the editor of the Lancet, "is party to a war crime of monstrous proportions. Yet our political consensus prevents any judicial or civil society response. Britain is paralysed by its own indifference." Such is the scale of the crime and of our "looking from the side".

As hysteria is again fabricated, for Iraq, read Iran. According to the former US treasury secretary Paul O'Neill, the Bush cabal decided to attack Iraq on "day one" of Bush's administration, long before 9/11 - and it beggars belief that Blair did not know that. The main reason was oil. O'Neill was shown a Pentagon document entitled Foreign Suitors for Iraqi Oilfield Contracts, which outlined the carve-up of Iraq's oilfields among the major Anglo-American companies. Under a law written by American and British officials, the Iraqi puppet regime is about to hand over the extraction of the largest concentration of oil on earth to Anglo-American companies.

Nothing like this piracy has happened before in the modern Middle East. Across the Shatt al-Arab waterway the other prize: Iran's vast oilfields. Just as non-existent weapons of mass destruction or facile concerns for democracy had nothing to do with the invasion of Iraq, so non-existent nuclear weapons have nothing to do with an American onslaught on Iran. Unlike Israel and the United States, Iran has abided by the rules of the Nuclear Non-Proliferation Treaty. The International Atomic Energy Agency (IAEA) has never cited Iran for diverting its civilian programme to military use. For the past three years IAEA inspectors have said that they have been allowed to "go anywhere". The recent security council sanctions against Iran are the result of Washington's bribery.

Until recently the British were unaware that their government was one of the world's most consistent abusers of human rights and backers of state terrorism. Few knew that British intelligence set out systematically to destroy secular Arab nationalism and in the 1980s recruited and trained young Muslims as part of a $4bn Anglo-American-backed jihad against the Soviet Union. The fuse of the bombs that killed 52 Londoners was lit by "us".

In my experience, most people do not contort their morality and intellect to comply with the double standards of rampant power and the media's notion of approved evil - of worthy and unworthy victims. They would, if they knew, grieve for all the lives, families, careers, hopes and dreams destroyed by Blair and Bush. The sure evidence is the British public's wholehearted response to the 2004 tsunami, shaming that of the government. Certainly, they would agree with Robert Jackson, the chief counsel of the United States at the Nuremberg trials of Nazi leaders. "Crimes are crimes," he said, "whether we do them or whether Germany does them, and we are not prepared to lay down a rule of criminal conduct which we would not be willing to have invoked against us."

Like Henry Kissinger and Donald Rumsfeld, who dare not travel to certain countries for fear of being prosecuted as war criminals, Blair as a private citizen may no longer be untouchable. On March 20 Baltasar Garzon, the tenacious Spanish judge who pursued General Pinochet, called for indictments against those responsible for "one of the most sordid and unjustifiable episodes in recent human history" - Iraq. Five days later, the chief prosecutor of the international criminal court, to which Britain is a signatory, said that Blair could one day face war-crimes charges.

These are critical changes in the way the sane world thinks - again, thanks to the reich of Blair/Bush. However, we also live in the most dangerous of times. On April 6 Blair accused "elements of the Iranian regime" of "financing, arming and supporting terrorism in Iraq". He offered no evidence, and the MoD has none. This is the same Goebbels-like refrain with which he and his coterie, Brown included, brought an epic bloodletting to Iraq. How long will the rest of us continue looking from the side?

· This is an edited version of an article in the current New Statesman; John Pilger's new film, The War on Democracy, will be previewed at the National Film Theatre in London on May 11 www.johnpilger.com